Grain Legumes and Green Manures for Soil Fertility in ... - cimmyt

To Laurence Jasi, et al.
C: One should not expect to see a significant effect
of legumes on Striga infestation after one crop. Our
experience in Western Kenya is that-the effects
require long term implementation of rotations since
the purpose of the legumes are to 1) stimulate
suicidal Striga germination, and 2) improve soil
fertility and biological activity to reduce the Striga
seed bank in soil. This requires several seasons of
rotation.
Q: Can crop models be used to predict the result of
this experiment?
A: There is some capacity in APSIM to look at crop
x weed interactions and weed management issues.
For parasitic weeds however, the model is not
parameterized (due to limited understanding of th'e
science) to handle parasitic weeds like Striga.
Q: Your treatments did not reduce Striga emergence
below that in the control, but your conclusion is not
that your hypothesis should be rejected, but that
more work is needed. Why not simply conclude
that green manures do not (in this case) usefully
reduce Striga emergence?
A: It is too early to make a conclusion. Green
manures can induce the suicidal germination of
Striga. With time the Striga seed bank is reduced. In
the long term, probably positive results may be
obtained.
To Paramu Mafongoya, et al.
Q: When is manure supposed to be called manure?
At times you have 10 t of material, of which 2 t is
organic manure and 8 t of sand!
A: Analyze the manure for sand and other materials
and then you can correct for sand.
Q: You have shown that incorporation of
leguminous tree biomass (e.g. Gliricidia) increased
pH significantly. There is some work from
Australia indicating that growing legumes acidifies
the soil significantly. Do you feel the cation/base
concentration in the tree biomass justifies the
increase in pH?
A: This is explained by leaching of N03 and
accompanying Mg2+ during the cropping phase
when there is no tree to recover N. In coppicing
fallows this explained the addition of cations in tree
biomass.
Q: How successful are agroforestry technologie's
such as improved fallows in improving soil fertility
in degraded soils like those in Kagoro in eastern ­
Zambia where ICRAF is located?
A: In Kagoro soils, mixtures of Glricidia and Sesbania
gave maize yields of 3 t/ha compared to 4 t/ha for
fully fertilized maize.
Q:
(1) It is good that now we are beginning to put
science to the observations of the benefits of
agroforestry trees that have been demonstrated
over the years.
(2) How could soil loss from runoff have been
measured in October as indicated by the data?
A: The data were collected by rainfall simulation
techniques.
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Grain legumes and Green Manures for Soil Fertility in Southern Africa